hi,ive got a simple exercise im going to try, i need to control 2, 0 to 10v's using just 1 10k pot just wondering if my circuit will work i intend using a quad lm324, also i was just wondering if i could control all 4 op amps using just 1 10k pot? (bottom circuit same as top sorry)

http://www.ti.com/lit/ds/symlink/lm324.pdfSee page 4 - see the PNP transistor that connects the output to Gnd? The closest you will is the Vce across that transistor.Could 3+mV depending on your operating conditions, multiplied by the gain of 2 you have set up (I believe Gain = 1 + R1/R2 for the noninverting amp as drawn).

yes my supply will be 12vdc, why wont it go to 0v lefty? whats the lowest v it will output?thanks

You would have to look at the datasheet for the opamp for the value. Unless it's a 'rail-to-rail' opamp it's output voltage can not reach down all the way to zero voltage rail unless that rail is a negative voltage.

An LM324 will go to 1.25 volts of either rail. If you require the posted schematic to go from 0 to 10V, try an LMC662 (Dual package) It has R/R Input (+/- .3V of supply rails) and Output. There is an LMC6684AIM which is a 12V part that has guarantee'd specs @ 10V. It "can" be accomplished with a '324 but it will require a +15 -5V supply to get the 0 and 10 v limits with a little margin.

Bob

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I'm thinking that will work ok, but what is your supply voltage? Hope it's at least 12V.

Yea, and probably won't output close to 0vdc without using a negative supply rail also.

Lefty

The inputs can go to -.3V according to the datasheet, it needs a couple of volts headroom on top though. That's why I mentioned 12V. What datasheet spec will tell me how close the output can get to 0V with a single supply? Another poster mentioned 1.25V, that seems a little high to me.

What datasheet spec will tell me how close the output can get to 0V with a single supply? Another poster mentioned 1.25V, that seems a little high to me.

Like I already said, the output can go right down to 0V provided you don't ask it to sink any current. That's why the first page of the datasheet http://www.ti.com/lit/ds/symlink/lm124-n.pdf says "Large output voltage swing 0V to V+ ? 1.5V". If you do ask it to sink current, you'll find the maximum sink current quoted at 2V and 0.2V output voltage on page 4.

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Make your life easier and just use rail-to-rail op-amps. The older parts have funky rules when it comes to getting close to the supply rails. You'll see the rail-to-rail terminology in the datasheet when it applies. Then you just need to look at supply voltage and input voltage numbers then. I have a bunch of Microchip MCP6021 and MCP6022 op-amps in my tinker box. They have a maximum operating voltage of 5V though. The MCP6023 has a /CS line for power saving.